U.S. patent application number 10/141911 was filed with the patent office on 2002-11-28 for laser beam machining method and apparatus.
Invention is credited to Ohta, Kazuyoshi, Sasano, Naoshige.
Application Number | 20020175151 10/141911 |
Document ID | / |
Family ID | 18991394 |
Filed Date | 2002-11-28 |
United States Patent
Application |
20020175151 |
Kind Code |
A1 |
Ohta, Kazuyoshi ; et
al. |
November 28, 2002 |
Laser beam machining method and apparatus
Abstract
Disclosed is a laser beam machining method and apparatus for
irradiating a work with a laser beam, to melt-evaporate the
irradiated region of the work at the irradiation spot. According to
the invention, a work such as an optical fiber can be machined into
a complicated form within a short period of time without accurately
controlling the laser beam irradiation position while inhibiting
the decline of machining accuracy due to thermal effect, by using a
mask having a light-transmitting section that is predetermined
times as large as the laser beam machining spot corresponding to
the form of the portion undergoing melt-evaporation of the
work.
Inventors: |
Ohta, Kazuyoshi;
(Miyamae-ku, JP) ; Sasano, Naoshige; (Sagamihara,
JP) |
Correspondence
Address: |
LAW OFFICES OF TOWNSEND & BANTA, P.C.
Suite 500, #50028
1225 Eye Street, N.W.
Washington
DC
20005
US
|
Family ID: |
18991394 |
Appl. No.: |
10/141911 |
Filed: |
May 10, 2002 |
Current U.S.
Class: |
219/121.69 ;
219/121.68; 219/121.73 |
Current CPC
Class: |
C03B 37/15 20130101;
C03B 23/099 20130101; B23K 26/0823 20130101; B23K 26/066 20151001;
G02B 6/2552 20130101 |
Class at
Publication: |
219/121.69 ;
219/121.73; 219/121.68 |
International
Class: |
B23K 026/36; B23K
026/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2001 |
JP |
2001-145613 |
Claims
What is claimed is:
1. A laser beam machining method, in which a work is irradiated
with a laser beam to melt-evaporate the portion irradiated with the
laser beam for machining the work, characterized in that a mask
having a light-transmitting section that is predetermined times as
large as the laser beam machining spot corresponding to the form of
the portion undergoing melt-evaporation of the work, is disposed
between a laser beam source and the work, and the laser beam
transmitted from a laser beam source through a beam-shaping optical
system is irradiated to said mask in a range larger than said
light-transmitting section of the mask, and the real image of the
light-transmitting section formed by the transmitted light is
reduced to the size of said machining spot by means of a reduced
image-forming optical system, to form the reduced image on the
work, for machining.
2. A laser beam machining method, according to claim 1, wherein the
work is relatively rotated around the axis perpendicular to the
laser beam irradiation axis, while the work is machined.
3. A laser beam machining method, according to claim 1 or 2,
wherein the real image-forming position is relatively moved alone
the laser beam irradiation axis, while the work is machined.
4. A laser beam machining method, according to any one of claims 1
through 3, wherein the work is an optical fiber, and for
irradiating the optical fiber with the laser beam from the lateral
face of the optical fiber, to machine the tip of the optical fiber,
the form of the machining spot is made to correspond to the form of
the tip observed when the optical fiber is viewed in the laser beam
irradiation direction.
5. A laser beam machining methods in which a work is irradiated
with a laser beam to melt-evaporate the portion irradiated with the
laser beam for machining the work, characterized in that a mask
with a quadrilateral light-transmitting section that is
predetermined times as large as a quadrilateral machining spot is
disposed between a laser beam source and the work, and the laser
beam transmitted from the easer beam source through a beam-shaping
optical system is irradiated to said mask in a range larger than
said light-transmitting a section, and the real image of the
light-transmitting section formed by the transmitted light is
reduced to the size of said machining spot by means of a reduced
image-forming, optical system, to form the reduced image on the
work, for machining.
6. A laser beam machining method, according to claim, wherein the
work is an optical fiber fixed in a glass capillary.
7. A laser beam machining method, according to claim 5 or 6,
wherein the real image-forming position is relatively moved along
the laser beam irradiation axis, while the work is machined.
8. A laser beam machining method, according to any one of claims 5
through 7, wherein the real image-forming position is relatively
reciprocated in the direction perpendicular to the laser beam
irradiation axis, while the work is machined.
9. A laser beam machining method, according to any one of claims 5
through 8, wherein in the case where the work is machined in the
direction crossing the axial direction of the work, the axial
direction of the work is set at the setting angle .alpha. expressed
by .alpha.=(.pi./2)+tan.sup- .-1(d/2f)-.beta. (where .beta. is the
angle of the face to be machined, against the work reference face
perpendicular to said axial direction; d is the width of the
transmitted light incident from the square light-transmitting
section of the mask on the reduced image-forming optical system;
and f is the focal distance of the reduced image-forming-optical
system) against the laser beam irradiation axis.
10. A laser beam machining method, according to any one of claims 1
through 9, wherein the laser beam to be irradiated is a multi-mode
beam having a flat beam profile.
11. A laser beam machining method, according to claim 10, wherein
the laser beam source is a TEA-CO.sub.2 laser.
12. A laser beam machining method, according to any one of claims 1
through 11, wherein the laser beam is irradiated to the work as a
pulsed beam.
13. A laser beam machining apparatus, characterized in that a mask
is disposed between a laser beam source and a work held by a
holding means; a light-transmitting section that is predetermined
times as large as the laser beam machining spot corresponding to
the form of the portion undergoing melt-evaporation of the work is
formed in the mask; a shaping optical system for irradiating, said
mask with a laser beam in a range larger than said
light-transmitting section is disposed on the laser beam source
side of the mask; and a reduced image-forming optical system for
reducing the real image of the light-transmitting section formed by
the laser beam passing through the light-transmitting section of
the mask to the size of said machining spot and for forming the
reduced image on the work, is disposed on the work side.
14. A laser beam machining apparatus, according to claim 13,
wherein the work holding means is a rotating means for rotating the
work around the axial direction of the work.
15. A laser beam machining apparatus, according to claim 13 or 14,
wherein a moving means for moving the real image-forming position
along the laser beam irradiation axis relatively to the work is
provided.
16. A laser beam machining apparatus, according to any one of
claims 13 through 15, wherein a means for reciprocating the real
image-forming position in the direction perpendicular to the laser
beam irradiation axis relatively to the work is provided.
17. A laser beam machining apparatus, according to any one of
claims 13 through 16, wherein the laser beam to be irradiated is a
multi-mode beam having a flat beam profile.
18. A laser beam machining apparatus, according to claim 17,
wherein the laser beam source is a TEA-CO.sub.2 laser.
19. A laser beam machining apparatus, according to any one of
claims 13 through 18, wherein the laser beam is irradiated to the
work as a pulse beam.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a laser beam machining
method and apparatus for irradiating a work with a laser beam, to
melt-evaporate the irradiated region of the work at the irradiation
spot. Particularly the present invention provides a laser beam
machining method and apparatus that can machine the tip portion of
an optical fiber, as an example of the work, into a desired
form.
BACKGROUND OF THE INVENTION
[0002] Optical fibers, for example, optical fibers mainly composed
of quartz glass are used in optical transmission systems and other
optical systems, and the tip forms of these optical fibers play an
important role irrespective of kinds of fibers such as single mode
fibers and multi-mode fibers.
[0003] It is desired that the end faces of an optical fiber have an
especially smooth surface and an accurate form for minimizing the
connection loss in its connection with another optical fiber or an
active device. Therefore, it is desired that the method of
machining the tip of an optical fiber can achieve accurate
machining into a predetermined form at high productivity
[0004] Known methods of finely processing the tip of an optical
fiber include mechanical methods such as fiber cleaving, chemical
methods such as etching and optical methods such as the use of a
CO.sub.2 laser, etc.
[0005] The mechanical method using a fiber cleaver allows the tip
of an optical fiber to be simply and sharply cleaved, but has a
problem that it cannot process the tip into a semi-spherical,
conical, or wedge-like surface, etc.
[0006] The chemical method using etching allows the tip of an
optical fiber to be formed as desired, but since it is difficult to
control the form and takes a long period of time, the method has a
problem in view of productivity.
[0007] In the case where the conventional general method of using a
CO.sub.2 laser is used to cut an optical fiber to process it at an
end, it can happen that the heat generated during machining causes
a form error, and since the spatial distribution of light
intensities is Gaussian, there is such a problem that the machined
edge becomes blunt.
[0008] Examples of these cases are described below.
[0009] For example, in the optical fiber cutting methods and
apparatuses described in the gazettes of JP02-230205A and
JP02-238406A, optical fibers are mechanically cut. These methods
allow optical fibers to be cut easily and well, but cannot be used
for processing the tips of optical fibers.
[0010] EP 0987570 discloses a method of cutting an optical fiber
using a pulse CO.sub.2 laser. In this method, a circular laser beam
with Gaussian-distributed light intensities is merely condensed by
a lens for cutting an optical fiber. The method cannot process the
tip of the optical fiber into a desired form.
[0011] U.S. Pat. No. 5,256,851 discloses a method of
melt-evaporating the tip of an optical fiber very little by very
little using a pulsed CO.sub.2 laser. This method has such problems
that it takes a long period of time for predetermined
machining.
[0012] In the above-mentioned machining method using a pulsed
CO.sub.2 laser, since the tip of an optical fiber to be differently
formed depending on the applicable specifications must be processed
into a desired form by repeating micro machining, the laser beam
must be finely condensed like a point using a lens, for accurate
processing into a desired form.
[0013] Therefore, the control of the laser beam irradiation
position for adaptation to the form to be obtained at the tip of
the optical fiber is troublesome, and expensive equipment is
necessary for very highly accurate irradiation position
control.
[0014] In addition, the spatial distribution of light intensities,
i.e., profile of the light condensed by a lens becomes conical with
the focus as the vertex, machining becomes difficult with the
increase in the depth of the machined portion of the optical fiber.
Furthermore, there is such a problem that since a thin V-shaped end
face is formed in the section of the machined portion, the gas,
fume and heat generated during machining are likely to be retained
there, to contaminate or curve the machined surface.
[0015] Furthermore, if the pulsed CO.sub.2 laser is used, since the
tip of an optical fiber is irradiated with a laser beam having high
light intensity continuously for a long time, the peripheral
portion of the tip portion is also heated to deform the optical
fiber, not allowing machining as designed. Moreover, if a pulse
laser is used, the thermal effect on the optical fiber can be
reduced, but there is another problem that the machining time
becomes longer by that.
OBJECTS OF THE INVENTION
[0016] One of the objects of this invention is to provide a laser
beam machining method and apparatus that can machine the tip of a
work such as an optical fiber into a desired form highly accurately
within a short period of time.
[0017] Another object of this invention is to provide a laser beam
machining method and apparatus capable of preventing the vibration
of the fiber caused by the ablation during laser beam irradiation
and preventing the occurrence of facial sagging, that respectively
lower the form accuracy at the cut face when the tip of an optical
fiber is cut by means of laser beam machining.
SUMMARY OF THE INVENTION
[0018] To solve the above-mentioned problems, the present invention
proposes a laser beam machining method, in which a work is
irradiated with a laser beam to melt-evaporate the portion
irradiated with the laser beam for machining the work,
characterized in that
[0019] a mask having a light-transmitting section that is
predetermined times as large as the laser beam machining spot
corresponding to the form of the portion undergoing
melt-evaporation of the work, is disposed between a laser beam
source and the work, and
[0020] the laser beam transmitted from a laser beam source through
a beam-shaping optical system is irradiated to said mask in a range
larger than said light-transmitting section, and the real image of
the light-transmitting section formed by the transmitted light is
reduced to the size of said machining spot by means of a reduced
image-forming optical system, to form the reduced image on the
work, for machining.
[0021] According to this method, since the light-transmitting
section that is predetermined times as large as the machining spot
corresponding to the form of the portion undergoing
melt-evaporation of the work is formed in the mask irradiated with
a laser beam, the laser beam irradiated in a range larger than the
light-transmitting section passes through the light-transmitting
section of the mask, to become a beam with a spot form equal to the
form of the light-transmitting section.
[0022] This beam passes through a reduced image-forming optical
system, and as a result, the real image of the light-transmitting
section is reduced to the size of said machining spot, to form the
reduced image on the work. The portion of the work in the range of
the machining spot is melt-evaporated, and the portion not
melt-evaporated remains as a desired form.
[0023] In this case, if the laser beam passes through the
light-transmitting section formed in the mask, the light intensity
at the edge portion of the optical beam becomes high due to light
interference. So, the portion undergoing melt-evaporation can be
well molten also at the area corresponding to the boundary with the
portion undergoing no melt-evaporation, and the thermal effect on
the portion undergoing no melt-evaporation is small.
[0024] As described above, simply by forming the light-transmitting
section of the mask with a large area as desired, the real image of
the light-transmitting section can be reduced to the size of said
machining spot, to form the reduced image on the work. So, when the
work is machined, it is not necessary to control the laser beam
irradiation position each time.
[0025] Furthermore, since the laser beam is not condensed like a
point on a work for irradiation as in the conventional method, but
is irradiated as said machining spot corresponding to the form of
the portion undergoing melt-evaporation, the portion undergoing
melt-evaporation can be melt-evaporated generally as a plane not as
a point, and the predetermined machining can be accomplished within
a short period of time.
[0026] This invention also proposes a laser beam machining method,
in which a work is irradiated with a laser beam to melt-evaporate
the portion irradiated with the laser beam for machining the work,
characterized in that
[0027] a mask with a quadrilateral light-transmitting section that
is predetermined times as large as a quadrilateral machining spot
is disposed between a laser beam source and the work, and
[0028] the laser beam transmitted from the laser beam source
through a beam-shaping optical system is irradiated to said mask in
a range larger than said light-transmitting section, and the real
image of the light-transmitting section formed by the transmitted
light is reduced to the size of said machining spot by means of a
reduced image-forming optical system, to form the reduced image on
the work, for machining.
[0029] In this case, if the real image-forming position is moved
relatively along the laser beam irradiation axis, while the work is
machined, the image-forming face can be made to agree with the
machined face at each position in the depth direction of the work.
So, a well-machined face can be obtained without lowering the
machining speed.
[0030] Furthermore, if the real image-forming position is
reciprocated relatively in the direction perpendicular to the laser
beam irradiation axis, while the work is machined, the machining
method of this invention can be adapted to a large work.
[0031] Moreover, in the case where a work is machined in the
direction crossing the axial direction of the work, if the axial
direction of the work is held at a setting angle .alpha. expressed
by
.alpha.=(.pi./2).vertline.tan.sup.-1(d/2f)-.beta.
[0032] (where .beta. is the angle of the face to be machined
against the work reference face perpendicular to said axial
direction, d is the width of the transmitted light incident from
the quadrilateral light-transmitting section of the mask on the
reduced image-forming optical system, and f is the focal distance
of the reduced image-forming optical system) against the laser beam
irradiation axis, the face to be machined of the work can be
machined at a desired angle.
[0033] If the work is relatively revolved around the axis
perpendicular to the laser beam irradiation axis, when machined, a
surface of revolution such as a semi-spherical surface, conical
surface or paraboloid of revolution can be formed.
[0034] If the real image-forming position is relatively moved along
the laser beam irradiation axis while the work is machined, or if
the real image-forming position is relatively reciprocated in the
direction perpendicular to the laser beam irradiation axis, when
machined, then the work can be adequately machined, depending on
the kind and form of machining, the width, thickness and size of
the portion to be machined, etc.
[0035] The work can be, for example, an optical fiber, and the tip
of the optical fiber can be machined variously. If the optical
fiber is, for example, fixed in a glass capillary, when machined,
it is possible to prevent the vibration of the fiber caused by the
ablation during laser beam irradiation and to prevent the
occurrence of facial sagging that respectively lower the form
accuracy at the cut face formed by laser beam machining, etc.
[0036] The present invention also proposes a laser beam machining
apparatus for applying the above-mentioned method, characterized in
that a mask is disposed between a laser beam source and a work held
by a holding means; a light-transmitting section that is
predetermined times as large as the laser beam machining spot
corresponding to the form of the portion undergoing
melt-evaporation of the work is formed in the mask; a shaping
optical system for irradiating said mask with a laser beam in a
range larger than said light-transmitting section is disposed on
the laser beam source side of the mask; and a reduced image-forming
optical system for reducing the real image of the
light-transmitting section formed by the laser beam passing through
the light-transmitting section of the mask, to the size of said
machining spot, and for forming the reduced image on the work, is
disposed on the work side.
[0037] The laser beam machining apparatus can have a constitution
in which the work holding means is provided with a rotating means
for rotating the work around its axial direction, or a constitution
in which a moving means for moving the real image-forming position
along the laser beam irradiation axis relatively to the work is
provided, or a constitution in which a moving means for
reciprocating the real image-forming position in the direction
perpendicular to the laser beam irradiation axis relatively to the
work is provided.
[0038] It is preferred that the laser beam for machining as
described above is a multi-mode beam having a flat beam profile,
and the light source can be, for example, a TEA-CO.sub.2 laser
(Transverse Excited Atmosphere CO.sub.2 laser).
[0039] If a pulsed laser beam is used as the laser beam, the
above-mentioned thermal effect can be further inhibited to improve
the machining accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The numerous objects and advantages of the present invention
may be better understood by those skilled in the art by reference
to the accompanying Figures, in which:
[0041] FIG. 1 is an illustrative perspective view showing an
example of the laser beam machining apparatus for applying the
laser beam machining method of the present invention, and
illustrating its action.
[0042] FIGS. 2 are illustrative perspective views showing tip forms
of optical fibers and masks for obtaining the tip forms by means of
the machining of this invention.
[0043] FIG. 3 is an illustrative perspective view showing another
example of the laser beam machining apparatus for applying the
laser beam machining method of this invention, and illustrating its
action.
[0044] FIGS. 4 are illustrations showing a firer other example of
the laser beam machining apparatus for applying the laser beam
machining method of this invention, and illustrating its
action.
[0045] FIGS. 5 are illustrations showing a still further other
example of the laser beam machining apparatus for applying the
laser beam machining method of this invention, and illustrating its
action.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0046] In reference to FIGS. 1 to 3, an example of this invention
is described.
[0047] Symbol 1 indicates the laser beam machining apparatus of
this invention generally as an example of applying the apparatus
for machining an optical fiber. The laser beam machining apparatus
1 is generally composed of a laser beam supply 2 consisting of a
pulse TEA-CO.sub.2 laser 3 as a laser beam source and a magnifying
collimator lens system 4 as a beam-shaping optical system, a
rotatable holding member 6 for holding an optical fiber 5 as a
work, a mask 7 disposed between the laser beam supply 2 and the
optical fiber 5, and a convex lens 8 as a component of a reduced
image-forming optical system disposed between the mask 7 and the
optical fiber 5.
[0048] The laser beam machining apparatus 1 machines the tip of the
optical fiber 5, and in the drawings, the machined tip of an
optical fiber 5 is expressed by a solid line, and the non-machined
tip of an optical fiber 5 is expressed by a one-dot-dash line.
Therefore, the portion expressed by the one-dot-dash line indicates
the portion undergoing melt-evaporation 9 to be melt-evaporated by
laser beam machining, and the portion not to be melt-evaporated,
i.e., the portion undergoing no melt-evaporation is the tip of the
optical fiber 5 to be machined as desired.
[0049] The mask 7 has a light-transmitting section 11 that is
predetermined times as large as a laser beam machining spot 10
corresponding to the form of the portion undergoing
melt-evaporation 9 of the optical fiber 5, and the real image of
the light-transmitting section 11 formed by the light passing
through the mask 7 is reduced by the convex lens 8 provided as the
reduced image-forming optical system, to the size of said machining
spot 10, for forming the reduced image at the tip of the optical
fiber 5. Particular examples of the constitution will be described
later in detail.
[0050] In the above constitution, the laser beam irradiated from
the TEA-CO.sub.2 laser 3, passing through the magnifying collimator
lens 4 and shaped to a parallel beam with an area larger than said
light-transmitting section 11 is irradiated to the mask 7, passes
through the light-transmitting section 11, is reduced by the convex
lens 8 to the size of said machining spot 10, and is irradiated to
the tip of the optical fiber 5, to form the real image of the
light-transmitting section 11 of the mask 7 on the optical fiber 5,
thereby melt-evaporating the portion undergoing melt-evaporation 9
corresponding to the form of the light-transmitting section 11, for
machining.
[0051] In this machining, in the case where the holding member 6 is
not rotated, the tip of the optical fiber 5 is irradiated with the
laser beam in one direction, and is machined in the direction.
However, in the case where the holding member 6 is rotated, the tip
of the optical fiber 5 is irradiated with the laser beam in plural
directions of the circumference, and as a result, the surface of a
revolving body can be formed at the tip of the optical fiber 5 by
means of machining. The rotation of the holding member 6 can be
either continuous or stepwise.
[0052] In the above case, a pulse TEA-CO.sub.2 laser 3 is used as
the laser beam source as described above, and the TEA-CO.sub.2
laser 3 has a large peak power, and can deliver a multi-mode beam
with a flat beam profile as short pulses having a sharp rise.
Therefore, since large optical pulse energy can be applied to the
portion undergoing melt-evaporation 9 of the optical fiber 5 within
a short period of time, the portion undergoing no melt-evaporation
is not thermally affected, and only the portion undergoing
melt-evaporation 9 can be melt-evaporated for predetermined
machining.
[0053] Furthermore, for example, it is desirable that the
TEA-CO.sub.2 laser 3 is operated at a peak power of 1 to 10,000 kW,
a pulse width of 0.1 to 50 .mu.s and an oscillation wavelength of 9
to 11 .mu.m. For example, the optimum values for machining a quartz
optical fiber 5 as a work were 200 kW in peak value, 0.2 .mu.s in
pulse width and 10.6 .mu.m in oscillation wavelength
[0054] Moreover, the TEA-CO.sub.2 laser 3 is designed, for example,
to operate at irradiation intervals of 100 Hz or less. In the case
of operation at 100 Hz, where a laser beam with the largest pulse
width of 50 .mu.s is irradiated intermittently required times, the
duty ratio is 0.5%, and after laser beam irradiation for 50 .mu.s,
9950 .mu.s is the quiescent time. Since the duration of the
quiescent time becomes a cooling time, the heat generated by the
laser beam escapes during the time, and heat is unlikely to be
accumulated in the portion undergoing no melt-evaporation.
[0055] Particular examples of the predetermined form of the optical
fiber 5 to be machined and the form of the light-transmitting
section 11 of the mask 7 are explained below in reference to FIGS.
2.
[0056] FIG. 2 (a) shows a case where the tip of the optical fiber 5
is formed like a wedge by laser beam irradiation in one direction
as shown on the left in the drawing, or formed like a cone by
several times of laser beam irradiation with the rotation of the
holding member 6. The machining spot 10 of the laser beam in this
case has such a form as to ensure that a wedge portion 5a or a
conical portion 5b as the portion undergoing no melt-evaporation of
the optical fiber 5 is not irradiated with the laser beam, and that
only the portion undergoing melt-evaporation on the tip side and
outside of the portion undergoing no melt-evaporation is irradiated
with the laser beam. In correspondence to the machining spot 10,
the light-transmitting section 11 of the mask 7 has a form, in
which a triangular light-intercepting portion 7a corresponding to
the wedge portion 5a or the conical portion 5b on the tip side of
the optical fiber 5 is provided in a rectangular opening.
[0057] FIG. 2 (b) shows a case where the tip of the optical fiber 5
is formed to be semi-cylindrical by laser beam irradiation in one
direction as shown on the left in the drawing, or to be
semi-spherical by plural times of laser beam irradiation with the
rotation of the holding member 6. The machining spot 10 of the
laser beam in this case has such a form as to ensure that a
semi-cylindrical portion 5c or a semi-spherical portion 5b as the
portion undergoing no melt-evaporation of the optical fiber 5 is
not irradiated with the laser beam, and that only the portion
undergoing melt-evaporation 9 on the tip side and outside of the
portion undergoing no melt-evaporation is irradiated with the laser
beam. In correspondence to the machining spot 10, the
light-transmitting section 11 of the mask 7 has a form, in which a
semi-circular light-intercepting portion 7b corresponding to the
semi-cylindrical portion 5c or the semi-spherical portion 5d on the
tip side of the optical fiber 5 is provided in a rectangular
opening.
[0058] FIG. 2 (c) shows a case where the tip of the optical fiber 5
is formed like a paraboloid by laser beam irradiation in one
direction as shown on the left in the drawing, or formed like the
surface of a paraboloid by plural times of laser beam irradiation
with the rotation of the holding member 6. The machining spot 10 of
the laser beam in this case has such a form as to ensure that the
paraboloid portion 5e or the rotating paraboloid surface portion 5f
as the portion undergoing no melt-evaporation of the optical fiber
5 is not irradiated with the laser beam, and that only the portion
undergoing melt-evaporation 9 on the tip side and outside of the
portion undergoing no melt-evaporation is irradiated with the laser
beam. In correspondence to the machining spot 10, the
light-transmitting section 11 of the mask 7 has a form, in which a
parabolic light-intercepting portion 7c corresponding to the
paraboloid portion 5e or the rotating paraboloid surface portion on
the tip side of the optical fiber 5 is provided in a rectangular
opening. This form is the same as that shown in FIG. 1.
[0059] The magnification of the light-transmitting section 11 in
reference to the machining spot 10 is described below. For example,
as shown in FIG. 2 in the case where the tip of an optical fiber 5
has a diameter of about 200 to 400 .mu.m is machined, if the size
of the mask 7 is 10 mm.times.10 mm, the maximum size of the
light-transmitting section 11 is about 8 mm.times.8 mm. So, the
magnification can be set at about 20 times.
[0060] In this case, since the convex lens 8 as the component of
the reduced image-forming optical system reduces the real image of
the light-transmitting section 11 to the size of the machining spot
10, for forming the reduced image on the work, the reduction ratio
is 1/20, an inverse number of said magnification.
[0061] To discuss the positional relation among the mask 7, the
convex lens 8 and the optical fiber 5, in the case where the convex
lens 8 as the component of the reduced image-forming optical system
has a focal distance f, it is only required that those components
are disposed to satisfy the following two formulae:
(l/f)=(l/a)+(l/b) . . . (1)
M=b/a . . . (2)
[0062] where a is the distance between the mask 7 and the convex
lens 8; b is the distance between the convex lens 8 and the optical
fiber 5; and M is the reduction ratio.
[0063] Based on the above, for example, the parameters in the case
where a paraboloid surface of 250 .mu.m in the longitudinal
direction is formed at the tip of an optical fiber 5 having a
diameter of 230 .mu.m are as described below.
[0064] At first, the machining spot 10 has such a form to ensure
that the rotating paraboloid surface portion 5f as the portion
undergoing no melt-evaporation of the optical fiber 5 is not
irradiated with the laser beam, and that only the portion
undergoing melt-evaporation 9 on the tip side and outside of the
portion undergoing no melt-evaporation is irradiated with the laser
beam. In correspondence to the machining spot 10, the
light-transmitting section 11 of the mask 7 has a form, in which a
parabolic light-intercepting portion 7c corresponding to the
rotating paraboloid surface portion 5f on the tip side of the
optical fiber 5 is provided in a rectangular opening as shown in
FIG. 1 and FIG. 2(c).
[0065] In this case, the machining spot 10 is set to have a size of
400 .mu.m.times.400 .mu.m sufficiently larger than the portion
undergoing melt-evaporation 9, to ensure that the portion
undergoing melt-evaporation 9 can be perfectly melt-evaporated. On
the other hand, the mask 7 used is provided with a
light-transmitting section 11 with a form 20 times as large as the
machining spot 10.
[0066] In this case, the required reduction ratio of the convex
lens 8 is M=1/20. If the focal distance of the convex lens 8 is
f=100 mm, then, from said formulae (1) and (2):
[0067] The distance between the mask 7 and the convex lens 8 is
a=2100 mm.
[0068] The distance between the convex lens 8 and the optical fiber
5 is b =105 mm.
[0069] So, those components should be disposed to satisfy these
positional relations.
[0070] With the components disposed like this, the optical fiber 5
is set in the holding member 6, and while the holding member 6 is
rotated, the laser beam source 3 is actuated to send pulses for
machining. In this case, the optical fiber 5 is rotated stepwise at
a predetermined angle, say, 30.degree., and while the fiber stops,
it is irradiated with the laser beam.
[0071] In this action, for example, a flat multi-mode laser beam
with 10.6 .mu.m wavelength, 0.2 .mu.s pulse width, almost square
spot form, and about 200 kW peak level is pulsed from the
TEA-CO.sub.2 laser 3, and it is shaped by the magnifying collimator
lens system 4 into a parallel beam with an almost square form 12 of
about 9 mm per side, and irradiated to the mask 7.
[0072] The laser beam passing through the light-transmitting
section 11 of the mask 7 becomes higher in the light intensity of
its edge portion due to light interference action, and falls on the
convex lens 8 used as the reduced image-forming optical system.
After it is condensed at the one focal point, an almost square real
image with a size corresponding to 1/20 of the size of the
light-transmitting section 11 is formed at the tip of the optical
fiber 5 to be machined.
[0073] In this state, the rotating paraboloid surface 5f as the
portion undergoing no melt-evaporation of the optical fiber 5 is
not irradiated with the laser beam, and only the portion undergoing
melt-evaporation 9 on the tip side and outside of the portion
undergoing no melt-evaporation is irradiated with the laser beam.
As a result, the machining spot 10 of about 400 .mu.m.times.400
.mu.m melt-evaporates the portion undergoing melt-evaporation 9, to
form a desired rotating paraboloid surface of 250 .mu.m in the
longitudinal direction at the tip of the optical fiber 5 having a
diameter of 230 .mu.m.
[0074] In this example, since a TEA-CO.sub.2 laser is used as the
laser beam source, a high output multi-mode beam with a flat beam
profile can be delivered in this case as shown in FIG. 1. So, even
if the optical fiber 5 is irradiated with a machining spot 10
relatively wider than in the conventional laser beam machining, the
portion undergoing melt-evaporation 9 can be well uniformly
melt-evaporated in the entire range to assure a high production
efficiency.
[0075] Moreover, if the laser beam passes through the
light-transmitting section formed in the mask, the light intensity
at the edge portion of the beam becomes high due to light
interference. So, the portion undergoing melt-evaporation can be
well molten also at the area corresponding to the boundary with the
portion undergoing no melt-evaporation, and the portion undergoing
no melt-evaporation is less thermally affected.
[0076] Furthermore, the laser beam can also be a continuous wave
beam as the case may be, but if a pulsed laser beam is used, the
portion undergoing no melt-evaporation of the optical fiber 5 is
little affected, and only the portion undergoing melt-evaporation 9
can be efficiently and reliably melt-evaporated and machined.
[0077] In the present invention as described above, simply by
forming the light-transmitting section of the mask with a large
area as desired, the real image of the light-transmitting section
can be reduced to the size of the machining spot and the reduced
image can be formned on the work. So, it is not necessary to
control the laser beam irradiation position accurately each time in
the machining of works.
[0078] In the example of the laser beam machining apparatus of the
present invention described above, when the work is relatively
rotated around the axis Fx perpendicular to the laser beam
irradiation axis Lx while being machined, the work is rotated, that
is, in this case, the holding member 6 of the optical fiber 5 is
rotated. However, on the contrary, the laser beam irradiation
system can also be rotated.
[0079] In FIG. 3, the optical fiber 5 as the work is fixed at the
center, and the irradiation system is disposed to rotate for
ensuring that the work is irradiated with the laser beam from the
circumference.
[0080] In the laser beam machining apparatus of FIG. 3, on the
extension line of the optical axis Lx of the beam-shaping optical
system and the optical axis Fx of the optical fiber 5, a mirror 13
is disposed, to bend the laser beam toward outside, and on the
extension line of the bent optical axis, a satellite mirror 14 is
disposed. And the mirror 13 and the satellite mirror 14 are
interlocked for rotation.
[0081] In this constitution, the laser beam irradiated from a laser
beam supply 2 is magnified by a beam-shaping optical system into a
parallel beam which passes through a light-transmitting section 11
of a mask 7 and bent in optical axis by the mirror 13 toward
outside, to pass through a convex lens 8. Then, it is again bent in
optical axis by the satellite mirror 14 toward inside, and
irradiated to the tip of the optical fiber 5 from just beside. In
this case, the reduced real image of the light-transmitting section
11 is formed on the optical fiber 5, for machining as described
before.
[0082] FIGS. 4 show a further other example of the laser beam
machining apparatus of this invention. In the laser beam machining
apparatus, the machining spot in the laser beam machining apparatus
of the example described above has a quadrilateral (square or
rectangular) form, and a mask 17 having a quadrilateral
light-transmitting section 21 that is predetermined times as large
as the machining spot 20 is disposed between a laser beam source
and the work 15, to ensure that the laser beam transmitted from a
laser beam source through a beam-shaping optical system is
irradiated to the mask 17 in a range 22 larger than said
light-transmitting section 21, and the real image of the
light-transmitting section 21 formed by the transmitted light is
reduced by a convex lens 18 as a reduced image-forming optical
system to the size of said machining spot 20, to form the reduced
image on the work 15, for machining.
[0083] In this example, the work 15 is an optical fiber as in the
above-mentioned example, but the optical fiber 15 is fixed in a
glass capillary 23.
[0084] If the work 15 is machined by means of the above-mentioned
laser beam machining apparatus, the facial sagging that occurs
without fail in the initial stage of laser beam irradiation occurs
on the surface of the glass capillary 23. So, there is a large
advantage that the end face of the optical fiber 15 held at the
center of the glass capillary 23 is not affected.
[0085] If the optical fiber 15 is machined by means of a pulse
CO.sub.2 laser without using the glass capillary 23, the machining
accuracy declines due to the very small vibration of the optical
fiber caused by the reaction of the ablation occurring on the
surface of the optical fiber when it is irradiated with the laser
beam. However, if the optical fiber 15 fixed in the glass capillary
23 is machined, it can be machined at high accuracy since the rigid
glass capillary 23 can inhibit the very small vibration of the
optical fiber 15.
[0086] It is preferred that the glass capillary 23 is made of
quartz glass, but a plastic capillary can also be used. The size of
the glass capillary 23 can be decided adequately, considering the
protection of the fiber inserted and fixed inside and the machining
time taken for machining with the laser beam. For example, an
adequate range is about 3 to 20 times the diameter of the optical
fiber 15.
[0087] On the other hand, the optical fiber 15 in the glass
capillary 23 is fixed using an adhesive, and though the material of
the adhesive is not especially limited since the adhesive is used
merely for fixing the optical fiber 15 to the capillary 23, an
epoxy adhesive is preferred for an application in which severe
temperature characteristics are required for a optical module,
etc.
[0088] It is preferred that the thickness of the adhesive layer is
as thin as possible, since the positional relation between the
optical fiber 15 inserted in the capillary 23 and the inner
diameter of the capillary 23 can be accurately specified, but if
the thickness is too small, the bonding strength declines. So, the
thickness of the adhesive can be decided considering these
conditions. The thickness of the adhesive layer, i.e., the
difference between the inner diameter of the capillary 23 and the
outer diameter of the optical fiber 15 can be, for example, about 1
.mu.m to 10 .mu.m.
[0089] In the laser beam machining apparatus, if the real
image-forming position is relatively reciprocated in the direction
perpendicular to the laser beam irradiation axis Lx, while the work
is machined, as shown in FIG. 5(a), (b), a large work 15 can be
machined.
[0090] In ordinary laser beam machining, a circular beam is
condensed by means of a lens, and the work is machined at the focal
point of the lens. In this case, since the spot size at the
condensed point is as small as ten-odd micrometers, the machined
portion becomes like a thin groove as the machining of the work
progresses in the thickness direction. In this case, the impurities
and the like contained in the work become gaseous or fumy fine
particles which are retained in the thin groove, and since they
absorb the laser beam, machinability becomes extremely lower as the
groove becomes deeper. Furthermore, the heat generated during
machining is accumulated to curve the machined surface.
[0091] On the contrary, in the present invention, the machining
spot is not like a point unlike the one in the conventional method,
but is a square or rectangular form having an area. Therefore, the
area to be machined can be large, and hence, the retention of gas
or fume generated during machining can be prevented, and the
inconvenience involved in the retention can be avoided.
[0092] On the other hand, if the position of the image-forming face
of said light-transmitting section is moved in the depth direction
with the progression of work machining, the machining speed does
not decline since the image-forming face can be always kept to
agree with the machined face.
[0093] For example, when a convex lens 18 as the component of the
reduced image-forming optical system was moved in the optical axis
direction Lx whenever a laser beam was irradiated using a square
machining spot of 200 .mu.m per side, for moving the image-forming
face for machining in the depth direction with the progression of
machining, as shown in FIG. 5(a) good machined faces could be
obtained.
[0094] As for the means for moving the image-forming face, instead
of the convex lens 18, any other component of the laser beam
irradiation system can be moved, or the work 15 can also be moved
in the direction of the laser beam irradiation axis Lx.
[0095] If the convex lens 18 is moved to move the real
image-forming face of the light-transmitting section, i.e., the
machining spot 20 in the depth direction of the work, the size of
the machining spot becomes smaller as the convex lens 18 is moved
in the depth direction of the work 15. As a result, the machined
face becomes inclined by a predetermined angle against the laser
beam axis.
[0096] For the inclination, the following was found. If the
inclination angle is .theta., the width of the transmitted light
incident on the lens 18 of the reduced image-forming optical system
from the light-transmitting section 21 of the mask 17 is d, and the
focal distance of the lens 18 is f, then the inclination angle
.theta. can be expressed by the following formula.
.theta.=tan.sup.-1(d/2f)
[0097] On the other hand, if machining is made as described above,
by inclining the optical axis Fx of the fiber by angle .alpha.
against the laser beam irradiation axis Lx, the angle .beta. of the
machined face against the work reference face perpendicular to the
optical axis Fx of the fiber 15 is 1 = ( / 2 ) + - = ( / 2 ) + tan
- 1 ( d / 2 f ) -
[0098] Formula
[0099] Therefore, in the case where the work 15 is machined in the
direction crossing the axial direction Fx of the work 15, in order
to obtain a desired value as the angle .beta. of the machined face
against the work reference face perpendicular to said axial
direction Fx, it is necessary that the axial direction Fx of the
work 15, i.e., the optical axis Fx of the fiber 15, if the work 15
is an optical fiber, is set at the setting angle .alpha. expressed
by
.alpha.=(.pi./2)+tan.sup.-1(d/2f)-.beta.
[0100] against the laser beam irradiation axis Lx.
[0101] For example, in the case where it is desired to let the
machined face agree with the work reference face perpendicular to
the optical axis Fx of the fiber 15, because of .beta.=0, it is
only required that the setting angle .alpha. is set at
.alpha.=(.pi./2)+tan.sup.-1(d/2f)
[0102] The above description of examples refers to the tip of an
optical fiber selected as the work, but the present invention is
not limited to it, and can be applied also to other desired
materials.
* * * * *